1. Technical Field
The present invention relates to an electrostatic latent image developing toner for developing electrostatic latent images on a latent image support in image output devices, such as copying machines, printers, or faxes, a toner production method, and an image forming device using the same.
2. Related Art
In image output devices, such as electrophotographic copying machines, printers, and faxes, the diameter of toner particles for use in image formation has been increasingly reduced in order to meet demands of increasing the resolution of printed image, increasing the gradation thereof, reducing the amount of waste toners, reducing the consumption energy by lowering fixing temperatures, etc.
However, a small-diameter particle toner is likely to scatter, which causes problems of scattering of the toner into image forming devices and occurrence of toner stain, and further it has become an object to prevent the toner from scattering into the air from the devices. Heretofore, techniques for suppressing toner scattering have been developed. With a reduction in a toner particle size, the importance of suppressing toner scattering has further increased.
The toner has two kinds of adhesive force, i.e., static electricity force in which the electric field can be controlled and van der Waals force in which the electric field cannot be controlled. A reduction in the toner particle size increases the ratio of the van der Waals force relative to the ratio of the static electricity force, and thus it has become difficult to control the toner by the electric field. Moreover, a reduction in the toner particle size increases air resistance relative to gravity sedimentation. Therefore, when the toner that cannot be controlled by the electric field scatters during development or the like, the toner is likely to scatter in the air outside devices while being carried by the air current from a cooling fan or the like of devices.
In contrast, concerns on influences of floating particulates in the air, particularly fine particles, on the health have increased. It is mentioned that the standard on fine particles having a diameter of 2.5 μm or lower causing diseases of respiratory organs or the like, which is referred to as PM2.5, has been added in the U.S. environmental standards or the WHO guideline. Also in Japan, considering that the discussion on the establishment of environmental standards is being advanced, it is significant to prevent toners having a particle size of 2.5 μm or lower from scattering in the air.
In order to separate particles having a specific particle size from the toner, it has been proposed to classify powder containing 50% by number or more of particles having a volume average particle size of 7 μm or lower by transporting a toner to a vertical cylindrical pot, allowing the pot to stand still for 2 hours, performing separation by sedimentation, and then opening a stopping valve of a nozzle disposed at the pot side surface to discharge 50% of the whole amount of the resultant as a supernatant liquid (e.g., JP-A-2002-28527). However, the method requires long time for standing still and sedimentation, and thus has posed problems in industrially producing a toner.
It has also been proposed to prepare a toner having a volume average particle size of 6 to 8 μm by applying a centrifuge force of 1000 to 3000G using a decanter type centrifuge having two functions of separation by sedimentation and filtration drying (e.g., JP-A-2004-133326).
According to the method, a toner having an average particle size of 6.5 μm is obtained, but a toner of 3 μm or lower is contained in a proportion as high as 6%, and thus the toner does not sufficiently meet the standard of PM2.5.
According to former toner classifying methods, it is required to allow a toner to stand still for a long time and the content of a toner having a particle size distribution of 3 μm or lower decreases before classification, but the reduction degree of the toner having a particle size of 3 μm or lower has not been sufficient.